Conservation is tricky, and I highly suggest that you consult a professional as it is very easy to cause new damage through poor technique or by using incompatible materials. (For example, if you were to put acrylic paint over oil paint, the acrylic would become crackled and flake off due to gases released by the oil paint below. As a second example, if you applied oil paint directly to the exposed canvas, the oil would eventually cause the canvas to rot.)
I am not a professional, but I did take a course in painting conservation while studying abroad in Florence, so I can outline the basics of what a conservator may do to save your painting.
- Document original state and damage with photographs and notes.
- Use UV light, xrays, or other methods to reveal aspects invisible to the naked eye. (ex. old varnishes, hidden layers, or specific elements indicative of which paint was used originally, etc).
- Clean the surface and remove any old varnishes.
- Treat the wood supports for insects if needed.
- If the canvas itself is too fragile, it may be transferred onto a new canvas and carefully re-attached onto its stretcher bars. (A process of gluing the old canvas onto a compatible new canvas support).
- To repair the cracking and missing sections, a thick plaster will be applied with a tiny spatula to fill the gaps. This will be scraped smooth with a scalpel and will be level with the original paint, making the surface appear smooth again. If the texture of the canvas or brushstrokes is evident in the surrounding areas, this will be imitated with the plaster.
- Gouache is then applied to the plastered areas, but in a more saturated and lighter color that the original. This will be the base for the next step and keep the finished repair from looking dull.
- Colored varnishes applied with tiny brushstrokes will match the repaired areas with the original color.
- A clear varnish may be applied at the end if appropriate.